How many articles start off by extolling the randomized clinical trial as the pinnacle of scientific evidence? The next sentence typically confronts the practical reality that randomized trials are simply not feasible in most cases. In the absence of definitive trials, technology assessment methodologies have been forced to rely on various types of observational studies--prospective cohort, case control, retrospective studies, cross-sectional and case studies--and a certain component of expert opinion/group judgement, as expressed either in the published medical literature or by the assessors themselves.